U.S. patent number 7,274,866 [Application Number 11/432,779] was granted by the patent office on 2007-09-25 for power tool and method for controlling a power tool.
This patent grant is currently assigned to C. & E. Fein GmbH. Invention is credited to Sigmund Braun, Boris Rudolf.
United States Patent |
7,274,866 |
Rudolf , et al. |
September 25, 2007 |
Power tool and method for controlling a power tool
Abstract
A power tool is disclosed comprising a controller for
controlling at least one operating parameter, a motor for driving a
tool, at least three switching elements which are coupled to the
controller, and a speed sensor for monitoring the speed of the
motor to generate a speed signal, which is fed to the controller.
The controller is configured so that, in dependence on the speed
signal, with simultaneous activation of a first and at least one
other of the switching elements, a control signal for changing the
operating parameter is output, and that, in dependence on the speed
signal, with activation of the first and at least one other
switching element, a control signal for modified changing of the
operating parameter is output (FIG. 2).
Inventors: |
Rudolf; Boris (Stuttgart,
DE), Braun; Sigmund (Kusterdingen, DE) |
Assignee: |
C. & E. Fein GmbH
(DE)
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Family
ID: |
34559643 |
Appl.
No.: |
11/432,779 |
Filed: |
May 11, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060255754 A1 |
Nov 16, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/EP2004/012545 |
Nov 5, 2004 |
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Foreign Application Priority Data
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Nov 11, 2003 [DE] |
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103 53 302 |
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Current U.S.
Class: |
388/824; 173/217;
318/245; 388/809; 388/937 |
Current CPC
Class: |
B25F
5/00 (20130101); H02P 25/14 (20130101); Y10S
388/937 (20130101) |
Current International
Class: |
H02P
7/288 (20060101) |
Field of
Search: |
;388/809,824,937
;318/254 ;173/217 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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33 17 398 |
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Nov 1984 |
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DE |
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33 29 971 |
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Mar 1985 |
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DE |
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38 12 771 |
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Oct 1989 |
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DE |
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29 26 111 |
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Nov 1989 |
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DE |
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39 16 355 |
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Dec 1989 |
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DE |
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40 27 135 |
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Sep 1995 |
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DE |
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0 808 018 |
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May 1996 |
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EP |
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1 073 191 |
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Jun 2000 |
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EP |
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1 284 427 |
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Jul 2002 |
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EP |
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2 217 480 |
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Oct 1989 |
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GB |
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Other References
International Preliminary Report; Aug. 22, 2006; 7 pages. cited by
other .
International Search Report, Feb. 25, 2005, 3 pages. cited by
other.
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Primary Examiner: Ip; Paul
Attorney, Agent or Firm: St. Onge Steward Johnston &
Reens LLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation application of co-pending
International Patent Application PCT/EP2004/012545 filed on Nov. 5,
2004 which claims priority of German patent application 103 53
302.8 filed on the Nov. 11, 2003 the contents of which is fully
incorporated by reference herewith.
Claims
What is claimed is:
1. A power tool comprising: a motor for driving a tool; a
controller for controlling the power tool; a first, a second and at
least a third switching element, said switching elements being
coupled to said controller; and a speed sensor for monitoring a
speed of the motor to generate a speed signal which is input to
said controller; wherein said controller is configured for
increasing said speed, if said speed signal indicates a speed
greater than zero, and if said first switching element and said
second switching element are activated simultaneously; and
decreasing said speed, if said speed signal indicates a speed
greater than zero, and if at least two switching elements are
activated simultaneously, at least one of which being different
from said first and second switching elements.
2. The power tool of claim 1, wherein said controller is configured
to keep said motor idle, if said speed signal indicates a speed
equal to zero.
3. The power tool of claim 1, wherein said controller is configured
in such a way that, with simultaneous activation of said switching
elements, the speed is continuously changed, until either a
threshold value is reached or at least one of said switching
elements is deactivated.
4. The power tool of claim 1, wherein said controller is configured
to change the speed of said motor by predetermined increments.
5. The power tool of claim 1, wherein said controller further
comprises a memory for storing a last-set desired speed value,
which is stored at the time of the deactivation of at least one of
said switching elements previously activated for speed setting.
6. The power tool of claim 5, wherein said memory is configured to
retain said last-set speed value even when the motor is at a
standstill or is switched off.
7. The power tool of claim 1, further comprising a housing having a
left-hand gripping region and a right-hand gripping region, and a
central region; wherein each of said switching elements comprises
an actuating member, a first actuating member of said first
switching element being arranged within said central region, second
and third actuating members of said second and third switching
elements being arranged within said left-hand and right-hand
gripping regions.
8. The power tool of claim 7, wherein said activating members
comprise flexible pushbuttons being configured for soft-touch
activation of said switching elements.
9. The power tool of claim 8 being configured as an angle grinder,
wherein said housing is formed substantially in a bar-shaped manner
and comprises a gearhead at one end thereof, said gearhead
supporting said first switching element, said second and third
switching elements being supported on said left-hand and right-hand
sides of said housing.
10. The power tool according of claim 9, wherein said housing is
dimensioned so as to allow grasping of the housing with one hand,
said flexible pushbuttons of said second and third switching
elements being arranged in a gripping region of a thumb on the one
side and of an index finger or middle finger on the other side.
11. The power tool of claim 8 being configured as a tool selected
from the group formed by an angle grinder and a drill, wherein said
housing is formed substantially in a pistol-shaped manner having a
pistol grip, a right-hand and a left-hand side, the pushbutton of
said first switching element being arranged in a center of said
pistol grip within a gripping region of an index finger, the
pushbuttons of said second and third switching elements being
arranged on said right-hand and left-hand sides.
12. The power tool of claim 1, further comprising a housing and a
fourth switching element being connected to said controller;
wherein two ones of said switching elements are arranged on a
left-hand side of said housing and two other ones of said switching
elements are arranged on a right-hand side of said housing; wherein
said controller is configured so that the speed is increased upon
activation of two of said switching elements arranged on a first
side selected from the group formed by the left-hand side and the
right-hand side, and so that the speed is decreased upon activation
of two other ones of said switching elements arranged on the other
side of the housing.
13. The power tool of claim 1, further comprising a housing, a
fourth switching element and a fifth switching element both of
which being connected to said controller; wherein said housing
comprises a central part, a left-hand part and a right-hand;
wherein said first switching element is arranged on said central
part of said housing; wherein two ones of said second, third,
fourth and fifth switching elements are arranged on the left-hand
part of the housing and two other ones of said second, third,
fourth and fifth switching elements are arranged on the right-hand
part of the housing; wherein said controller is configured so that
the speed is increased upon activation of said first switching
element and one of said two ones of said switching elements, and so
that the speed is decreased upon activation of said first switching
element and one of said other ones of said switching elements.
14. The power tool of claim 1, wherein at least one said switching
elements is selected from the group formed by: an optical switching
element comprising a light transmitting conductor for transmitting
a light beam emitted by a light source into a receiving conductor
and a an evaluation means for evaluating the light received by said
receiving conductor to generate a switching signal; and a
micro-switch lying in a signal circuit, while said controller is
configured to control said motor via a power-circuit.
15. A power tool comprising: a controller for controlling at least
one operating parameter of said power tool; a motor for driving a
tool; a first, a second and at least a third switching element,
said switching elements being coupled to said controller; and a
speed sensor for monitoring the speed of the motor to generate a
speed signal which is input to said controller; wherein said
controller is configured for outputting a first control signal for
modifying said operating parameter in a first way, if said speed
signal indicates a speed greater than zero and if said first
switching element and said second switching element are activated
simultaneously; and for outputting a second control signal for
modifying said operating parameter in a way different from said
first way, if said speed signal indicates a speed greater than zero
and, if at least two of said switching elements are activated
simultaneously, at least one of which being different from said
first and second switching elements.
16. The power tool of claim 15, wherein said operating parameter to
be controlled is the setting of right-hand/left-hand rotation, and
wherein said controller is configured for outputting a control
signal for setting the motor upon activation of a first switching
element and a second switching element to right-hand rotation and
for setting the motor to left-hand rotation upon activation of the
first and at least one other switching element different from said
first and second switching elements.
17. The power tool of claim 12, wherein said controller is
configured so as to allow a power-on of said motor only upon
simultaneous activation of at least two switching elements.
18. The power tool of claim 17, further comprising a housing having
a front-region and a rear-region, wherein said controller is
configured so as to allow a power-on of said motor only upon
simultaneous activation of a switching element arranged in said
front region and of a switching element arranged in said rear
region.
19. A method of controlling at least any operating parameter of a
power tool comprising a motor for driving a tool, a controller for
controlling the operation of the power tool, and at least three
switching elements being coupled to the controller for controlling
the operating parameter, the method comprising the following steps:
monitoring the speed of said motor; monitoring the operating states
of said switching elements; controlling said operating parameter in
dependence on the speed of the motor and the switching states of
the switching elements.
Description
BACKGROUND OF THE INVENTION
The invention relates to a power tool with a controller for
controlling at least one operating parameter, with a motor for
driving a tool, and also to a method for controlling a power
tool.
Power tools are often equipped with electronic controls for
controlling the rotational speed of the drive motor. Generally
serving here for the setting is an adjusting wheel or the like,
which can only be actuated poorly during the operation of the power
tool.
In the case of some power tools, however, it would be advantageous
if a speed adjustment could also take place during work, in
particular even under load. In addition, it would be advantageous
if, apart from the speed, other operating parameters could be
controlled in a simple way.
SUMMARY OF THE INVENTION
It is a first object to disclose a power tool and a method of
controlling a power tool whereby an operating parameter can be
controlled in a simple way.
It is a second object of the invention to disclose a power tool and
a method of controlling a power tool whereby an operating parameter
can be adjusted even during operation.
It is a third object to disclose a power tool and a method of
controlling a power tool that allow an easy handling and operation
of the power tool.
These and other objects are achieved according to the invention by
a power tool with a controller for controlling at least one
operating parameter, with a motor for driving a tool, with at least
three switching elements, which are coupled to the controller, and
with a speed sensor for monitoring the speed of the motor to
generate a speed signal, which is fed to the controller, the
controller being formed in such a way that, in dependence on the
speed signal, with simultaneous activation of a first and at least
one other of the switching elements, a control signal for changing
the operating parameter is output, and that, in dependence on the
speed signal, with activation of the first and at least one other
switching element, a control signal for modified changing of the
operating parameter is output.
The object is achieved furthermore by a method for controlling at
least one operating parameter of a power tool which has a motor for
driving a tool and at least three switching elements which are
coupled to a controller for controlling the operating parameter,
with the following steps: monitoring the speed of the motor;
monitoring the operating states of the switching elements;
controlling an operating parameter in dependence on the speed of
the motor and the switching states of the switching elements.
The object of the invention is completely achieved in this way.
This is so because, according to the invention, by monitoring the
speed of the motor on the one hand and the switching states of the
switching elements on the other hand, in dependence on the speed
and the sensed switching states of the switching elements, a
control signal for changing the operating parameter is output only
in the case of a specific combination, while a modified control
signal for modified changing of the operating parameter is output
in the case of a specific other combination.
In this way, at least two specific switching elements must be
simultaneously actuated and the motor must have a specific speed,
which may be equal to zero or greater than zero, in order that a
specific control signal for changing an operating parameter is
generated, while a modified control signal for other changing of
the operating parameter is output in the case of actuation of at
least one other switching element.
In this way there is great flexibility in the selection of the
operating parameters to be controlled and in the selection of the
switching combinations of different switching elements, in order to
output a specific control signal in dependence on the sensed speed
of the power tool. In particular if the controller comprises a
microprocessor, different control strategies for controlling one or
more operating parameters can be realized by software. The
operating parameter to be controlled may be, for example, the speed
of the motor. Furthermore, in the case of such power tools in which
switching over between right-hand rotation and left-hand rotation
is made possible, it is conceivable to control the
right-hand/left-hand rotation setting in dependence on the
switching states of specific switching elements. Apart from these
two possible operating parameters which can be monitored or
controlled according to the invention, the monitoring or setting of
further operating parameters is conceivable, involving for example
a switching-off torque of a screwdriver or a safety value at which
the power supply to the motor is interrupted in order to avoid a
state of overloading or possible risk.
According to a first refinement of the invention, the operating
parameter to be controlled is the speed of the motor, the
controller being formed in such a way that, with the motor running
(speed n>0) and with simultaneous activation of the first
switching element and a second switching element, a control signal
for reducing the speed is output, and, with the motor running and
with simultaneous activation of the first switching element and a
third switching element, a control signal for increasing the speed
is output.
Although it would not be ruled out in principle to allow a changed
setting of the desired speed even when the motor is stationary, it
is preferred for reasons of safety to allow such a setting only
during operation. This is also advantageous for the user, since he
can immediately perceive the changed setting of the speed directly.
This is even possible when working under load.
It is therefore preferred according to a further embodiment of the
invention that no control signal for changing the speed is output
when the motor is stationary.
According to a further embodiment of the invention, the controller
is formed in such a way that, with simultaneous activation of the
first and second switching elements or the first and third
switching elements, the desired value of the speed is continuously
changed, until either a threshold value is reached or at least one
of the switching elements is deactivated.
In this way, continuous changing of the desired speed value is made
possible, in order in this way to allow infinitely variable setting
of the desired speed value.
According to an alternative embodiment of the invention, the
controller is formed in such a way that, with simultaneous
activation of the first and second switching elements or the first
and third switching elements, the desired value of the speed is
changed by a predetermined speed increment, but at most until a
threshold value is reached, and that, for further changing of the
speed, the deactivation of at least one switching element and
subsequent activation of the first and second switching elements or
the first and third switching elements is required.
Even with such staged changing of the speed, or by secure holding
of the first switching element and alternative actuation of a
further switching element, a speed adjustment that is simple for
the user can be realized, it also being possible for specific,
predetermined speed stages to be set.
In an additional development of the invention, a memory means is
provided for storing a last-set desired speed value, which is
output by the controller at the time of the deactivation of at
least one of the switching elements previously activated for speed
setting.
The memory means may be formed here in such a way that a stored
desired speed value is retained even after the motor is at a
standstill or is switched off. In this way, a desired speed value
that has once been set is maintained during work with the power
tool, or, even after switching off and renewed switching on of the
motor, the tool is set again to the desired speed value.
Furthermore, after switching off, setting to a specific standard
speed value, which may possibly be permanently programmed in, or
may be stored by actuating a specific combination of switching
elements, is conceivable.
According to a further embodiment of the invention, an operating
parameter to be controlled is the setting of right-hand/left-hand
rotation, a control signal for setting the motor to right-hand
rotation being output with activation of a first and a further
switching element, and a control signal for setting the motor to
left-hand rotation being output with activation of the first and at
least one other switching element.
In principle, it is possible when using a microprocessor-controlled
controller for this switching over between right-hand and left-hand
rotation to be performed while the motor is already running. In
this case, the controller detects the switching-over signal, runs
the motor down to a speed of 0 and then changes over the direction
of rotation. Alternatively, the control may also be designed in
such a way that a control command by means of actuating the
switching elements is only accepted if the motor is stationary
(n=0). In this way, an operating concept that is clearly evident to
the user can be used.
According to a further embodiment of the invention, the power tool
has a housing which has a left-hand gripping region and a
right-hand gripping region, activating members for the second and
third switching elements being provided in the left-hand and
right-hand gripping regions.
In this way, the various switching elements can be mounted in the
gripping region for holding the power tool, in order in this way to
make particularly ergonomic operation possible.
According to a further refinement of the invention, the housing has
a central region, at which an activating member for the first
switching element is provided.
This allows the first switching element, which in the case of
various variants of the invention definitely has to be actuated in
order to initiate a changed setting of the operating parameter to
be controlled, to be arranged centrally in such a way that it can
be reached.
According to a further refinement of the invention, the activating
members for actuating the switching elements are formed as flexible
pushbuttons.
In this way, a particularly ergonomic design of the power tool can
be achieved.
According to a further refinement of the invention, which is
preferred in particular when the power tool is designed as an angle
grinder, the housing is formed substantially in a bar-shaped manner
and has at one end of the housing a gearhead, on which the first
switching element is mounted, while the second and third switching
elements are provided on the left-hand and right-hand sides of the
housing.
The housing is preferably dimensioned here in such a way that
grasping with one hand is made possible, the flexible pushbuttons
for the second and third switching elements being arranged in the
gripping region of the thumb on the one side and the index finger
or middle finger on the other side.
In this way, particularly ergonomic design and handling is made
possible, in particular for the case of an angle grinder.
According to an alternative embodiment of the invention, which is
advantageous in particular when the power tool is designed as a
screwdriver or drill, the housing is formed substantially in a
pistol-shaped manner, the pushbutton for the first switching
element being arranged in the center of a pistol grip in the
gripping region of the index finger and the pushbuttons for the
second and third switching elements being arranged on the
right-hand and left-hand sides of the housing.
In this way, holding of the power tool at the pistol grip can be
combined with deliberate actuation of the second and third
switching elements for adjusting the operating parameter, which is
made possible only with the other hand.
According to a further refinement of the invention, the power tool
has a fourth and a fifth switching element, the controller being
formed in such a way that the first switching element and
optionally the second or fourth switching element have to be
activated for increasing the speed and the first and optionally the
third or fifth switching element have to be activated for reducing
the speed.
The pushbuttons for activating the fourth and fifth switching
elements are preferably located here on the left-hand and
right-hand sides of the housing, at the end of the housing that is
opposite from the gearhead.
In this way, an adjusting possibility for setting the operating
parameter that can easily be remembered by a user can be
predetermined, for instance in such a way that at least one of the
two switching elements arranged on the left-hand side of the
housing must be actuated in combination with the first switching
element in order for instance to bring about a reduction of the
speed. Conversely, the first switching element and one of the two
switching elements arranged on the right-hand side of the housing
must then be actuated to increase the speed.
According to a further refinement of the invention, the controller
is formed in such a way that switching on of the motor is made
possible only with simultaneous activation of at least two
switching elements.
It is preferred here for the controller to be formed in such a way
that switching on of the motor is made possible only with
simultaneous activation of a switching element arranged in a front
region of the housing and a switching element arranged in a rear
region of the housing.
In this way it can be ensured that, when the power tool is seized
in the region of flexible buttons by means of which the assigned
switching elements can be activated, starting-up of the motor is
only made possible if a further pushbutton is actuated with a
second hand. In this way, increased safety is ensured, since
two-handed actuation is therefore necessary in order to start the
motor.
According to a further refinement of the invention, an optical
indicator element to display a set operating parameter is
provided.
This also has the effect of increasing safety and makes working
easier for the user, since it is optically evident at any time
which operating parameter has been set, that is to say for example
which desired speed has been set or whether right-hand/left-hand
rotation has been set.
According to a further refinement of the invention, at least one of
the switching elements is formed as an optical switching element,
by means of which a light beam which is emitted by a transmitting
conductor and fed to a receiving conductor is influenced and the
changing of the light signal coupled into the receiving conductor
is evaluated to generate a switching signal.
According to this measure, which is known per se in principle from
EP-A-1 284 427, a particularly ergonomic design of the power tool
can be achieved, since in this way a whole series of optical
switching elements can be arranged at different positions of the
housing, since no regard to special insulation from the power
voltage has to be paid here. Furthermore, the switching elements
can be miniaturized and durable actuation during operation can be
easily made possible by means of flexible pushbuttons.
Substantially similar results can be achieved if the switching
elements are formed as micro-switches which respectively lie in a
signal circuit.
A power element which, for controlling the motor, lies in a load
circuit may preferably be galvanically isolated from the
micro-switches here. This has the advantage that--as also in the
refinement with optical switching elements--no regard has to be
paid to regulations for protection with respect to galvanic
isolation from the power voltage. Therefore, the micro-switches
concerned, and also the optical switching elements, can be placed
particularly favorably from an ergonomic viewpoint.
As already mentioned, in an advantageous development of the method
according to the invention, the speed of the motor is controlled as
the operating parameter and a control signal for reducing the speed
is output with simultaneous activation of the first and a further
switching element, while the control signal for increasing the
speed is output with simultaneous activation of the first and
another switching element.
As likewise already mentioned, in an advantageous development of
the method according to the invention, the setting of
right-hand/left-hand rotation is controlled as the operating
parameter and a control signal for setting the motor to right-hand
rotation is output with activation of the first and a further
switching element, and a control signal for setting the motor to
left-hand rotation is output with activation of the first and at
least one other switching element.
If desired, starting-up of the motor can only be made possible if
at least two of the switching elements are activated
simultaneously.
According to a further refinement of the invention, a signal for
stopping the motor is generated with the motor running when
specific switching elements are deactivated, whereby braking of the
motor can be simultaneously initiated.
This allows increased safety to be ensured, in particular in the
case of those power tools which pose a relatively high potential
risk, such as for instance angle grinders, circular saws or the
like.
In conjunction with the necessary actuation of the first switching
element for activating the setting operation for the speed
adjustment and with the actuation of a switching element on the
right-hand side of the housing for increasing the speed and on the
left-hand side for reducing the speed, an operating concept that
can be remembered by the user is therefore obtained: for starting
the motor, two switching elements, in a front region and a rear
region of the housing, must be activated simultaneously, so that
deliberate switching on of the power tool is ensured, and running
of the motor when the power tool is simply grasped with one hand is
avoided. If the speed is then to be adjusted, the first switching
element in the middle of the housing is actuated with the motor
running and at the same time a switching element on the left-hand
or right-hand side of the housing is actuated to reduce or increase
the speed. The latter can be performed with the hand with which the
power tool is also held.
It goes without saying that the features of the invention mentioned
above and those still to be explained below can be used not only in
the combination respectively given but also in other combinations
or on their own without departing from the scope of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the invention emerge from the
description which follows of preferred exemplary embodiments and
with reference to the drawing, in which:
FIG. 1 shows a view from above of the first embodiment of a power
tool according to the invention in the form of an angle
grinder;
FIG. 2 shows a simplified basic circuit of the power tool according
to FIG. 1; and
FIG. 3 shows a side view of a further power tool according to the
invention in the form of a screwdriver or drill.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, a power tool according to the invention, which is
designed as an angle grinder, is designated overall by the number
10.
A simplified basic circuit of the power tool 10 according to FIG. 1
is designated overall in FIG. 2 by the number 36.
The power tool 10 has an elongate, approximately bar-shaped housing
12, at one end of which a gearhead 14 is provided, on the underside
of which a protective shroud 16 is mounted. Provided at the outer
end of the drive shaft protruding out from the gearhead is a holder
for receiving a tool 34 in the form of a grinding wheel or cutting
wheel. To the left or right, a stem handle 18 can be screwed onto
the gearhead 14, as can be seen from FIG. 1.
The region of the housing 12 that is formed symmetrically with
respect to its longitudinal axis and directly adjoins the gearhead
14 is narrowed on both sides, in order to form a gripping region,
on which the housing 12 can be easily gripped with one hand and can
be easily held by the thumb on one side and by the other fingers on
the other side. In the middle of the gearhead, approximately level
with the stem handle 18, there is an upwardly protruding first
pushbutton 20, by means of which a first switching element (cf.
number 21 according to FIG. 2) can be actuated. In the narrowing
region of the housing 12 which adjoins the gearhead 14 there are on
the left-hand and right-hand sides of the housing two flexible
pushbuttons, namely a second flexible pushbutton 22 and a third
flexible pushbutton 24. These flexible pushbuttons 22, 24 are
assigned switching elements 23, 25, which are activated by means of
them (cf. FIG. 2).
At the end region opposite from the gearhead 14 (approximately in
the outer third of the housing 12), a further narrowing of the
housing is provided on both sides. In the narrowing region, further
pushbuttons are provided on the left-hand side of the housing and
the right-hand side of the housing, namely a fourth pushbutton 26
on the left-hand side and a fifth pushbutton 28 on the right-hand
side. Further switching elements 27, 29 can be actuated by means of
these pushbuttons 26, 28 (cf. FIG. 2).
According to the basic circuit 36 according to FIG. 2, the motor 42
lies in a power circuit 40. The motor 42 is supplied with voltage
from a voltage source 38 (230 V AC voltage) via a power switching
element 44, for example in the form of a triac. If appropriate, an
on/off switch, by which the appliance is put into operation (not
represented), may be additionally provided in the load circuit 40.
The switching elements 21, 23, 25, 27, 29 take the form of
micro-switches or optical switches and are respectively connected
to a common control circuit 48. In the case of the embodiment
represented as a micro-switch, each of the switching elements 21 to
29 lies in a signal circuit which can be closed by the switching
element concerned.
As a preferred variant (not graphically represented), each of the
switching elements 21, 23, 25, 27, 29 may also be formed as an
optical switching element, which optically influences a light
signal which is fed via a transmitting conductor and evaluated by
means of a receiving conductor.
This allows simple spring-loaded sensing elements, by which the
light beam can be interrupted, to be provided for instance at two
ends lying opposite each other of the transmitting conductor and
the receiving conductor. For details, reference is made in this
regard to US patent application published as US 2003/0034164 A1,
the content of which is fully incorporated by reference.
Since the switching elements 21 to 29 in the form of optical
switching elements or micro-switches are preferably galvanically
isolated from the load circuit 40, shock protection is obtained
irrespective of where the switching elements concerned are
integrated in the power tool. In this way it is made possible to
arrange the switching elements concerned, with the assigned
flexible pushbuttons, at the locations that are particularly
favorable ergonomically, as explained above on the basis of FIG.
1.
Furthermore, the circuit 36 according to FIG. 2 has a speed sensor
(tachogenerator) 46, by means of which the speed of the motor shaft
or of an output shaft which is connected to it by means of a gear
mechanism and on which the tool holder is provided is monitored.
The output signal of the speed sensor 46 is digitized and fed to
the controller 48. The preferably microprocessor-controlled control
unit 48 monitors all the safety functions of the power tool 10,
controls the power output or speed of the motor 42 by means of the
power switching element 44 and makes possible the setting of
specific operating parameters in dependence on the switching state
of the switching elements 21, 23, 25, 27 and 29 and in dependence
on the speed signal obtained.
The microprocessor of the controller 48 is then programmed in such
a way that an adjustment of the desired speed can only be performed
with the motor running, to be precise by the first pushbutton 20
and one of the pushbuttons 22, 24, 26, 28 being pressed
simultaneously, in order to actuate the assigned switching element
21, 23, 25, 27, 29. Here, the switching elements 23, 27, which are
assigned to the pushbuttons on the left-hand side of the housing,
are provided in connection with the switching element 21 for
lowering the desired speed, while the switching elements 25, 29,
which are assigned to the pushbuttons 24, 28 on the right-hand side
of the housing, serve in connection with the switching element 21
for increasing the desired speed. If, therefore, the speed sensor
signals a running motor (n>0), actuation of the first pushbutton
20 in combination with the second pushbutton 22 and/or the fourth
pushbutton 26 leads to a reduction of the desired speed, until a
lower threshold value is reached. If, on the other hand, the first
pushbutton 20 is actuated in connection with the third pushbutton
24 and/or the first pushbutton 28, an increase of the desired speed
is obtained, until an upper threshold value is reached. If the
pushbutton 20 or one of the other pushbuttons is released and only
a single pushbutton 22, 24, 26 or 28 is then activated, the
last-set desired speed value is stored. This desired speed value is
also set after the tool is switched off and started up again
later.
It goes without saying that, whenever reference is made here to a
desired speed value, this can only be achieved during idling and
that other speeds are of course obtained under loading.
According to FIG. 1, serving for displaying the desired speed is an
indicator element 30, which is located on the upper side of the
housing 12, approximately midway between the two pushbuttons 26 and
28. The indicator element contains three LEDs 31, 32, 33, which are
arranged one behind the other. The indicator element 30 has a
viewing area, which tapers such that it is more slender toward the
end opposite from the gearhead 14 and widens toward the other side.
This allows a total of five speed settings to be optically
displayed. If only the LED 33 lights up, this indicates the lowest
speed. If the middle LED 32 lights up, this indicates a moderate
speed, if only the LED 31 toward the gearhead 14 lights up, this
indicates the maximum speed. If both the LED 31 and the LED 32
light up, this shows an intermediate value between a moderate speed
and the highest speed. If the LED 32 and the LED 33 light up, this
indicates an intermediate value between the moderate speed and the
lowest speed.
As a consequence of the optical switches or micro-switches that are
used, the switching elements 21, 23, 25, 27, 29 can be operated
with extremely little expenditure of force via the assigned
flexible pushbuttons 20, 22, 24, 26, 28, which may consist for
instance of a yielding plastic. The power tool 10 can therefore be
held with one hand by grasping the housing 12 at the narrowing
before the transition to the gear head 14, the thumb resting on the
pushbutton 22 on the left-hand side of the housing and the fingers
lying on the pushbutton 24 on the right-hand side of the housing
when it is grasped with the right-hand.
The switching logic which the control unit 48 has is then
programmed in such a way that starting-up of the tool is only made
possible when, in addition to one of the two switching elements 23,
25, which are actuated by means of the front pushbuttons 22, 24, a
switching element 27 or 29 is also actuated by means of a
pushbutton 26, 28 in the rear region of the housing 12. This is
conceived as a safeguard against starting-up of the power tool 10
when it is simply grasped with one hand, since a second hand is
necessary for the actuation of the rear switching element, and
consequently two-handed actuation is required for starting-up the
power tool 10. After starting-up of the motor 42, the activation of
any switching element 23, 25, 27, 29 is sufficient to keep the
motor in operation. If, however, all the pushbuttons 22, 24, 26, 28
are released, the power switching element 44 blocks completely, so
that the tool runs down. If appropriate, braking may be
additionally realized in an electronic way. On the other hand, the
switching element 21, which can be activated by means of the
pushbutton 20, is provided only for the activation of the speed
adjustment. If the switching element 21 is activated by pressing
the pushbutton 20 and at the same time a switching element 23 or 27
on the left-hand side of the housing or a switching element 25 or
29 on the right-hand side of the housing, either a speed reduction
or speed increase is initiated, which takes place continuously
until the switching element 21 is released again or else a lower or
upper threshold value is reached.
If, on the other hand, the switching element 21 and at the same
time a switching element 23 or 27 on the left-hand side of the
housing and a switching element 25 or 29 on the right-hand side of
the housing are activated, no change of speed takes place.
In FIG. 3, a further exemplary embodiment of a power tool according
to the invention is represented and designated overall by the
number 50. This power tool 50 is designed as a screwdriver or drill
with a pistol-shaped housing 52 and has a pistol grip 54. Provided
in the middle of the pistol grip 54, level with the region which
can be enclosed by the index finger, is a pushbutton 60, by means
of which an assigned switching element can be actuated. At the
upper end, opposite from the tool holder 56 of the drive shaft, a
flexible pushbutton is respectively provided on the right-hand and
left-hand sides of the housing. In this respect, only the
pushbutton 62 on the left-hand side of the housing can be seen in
FIG. 3, while the corresponding pushbutton on the right-hand side
of the housing cannot be seen of course. Since a screwdriver or
drill does not present any particular potential risk, as for
instance in the case of an angle grinder, the controller may then
be designed here in such a way that, when there is actuation of the
switching elements assigned to the pushbutton 60, starting-up of
the motor immediately takes place. The pushbutton 62 on the
left-hand side of the housing or the assigned pushbutton on the
right-hand side of the housing can then be used for speed
adjustment, with simultaneous actuation of the pushbutton 60. As
also in the case of the embodiment of the power tool 10 according
to FIG. 1, in this case once again a speed reduction preferably
takes place with actuation of the pushbutton 62 on the left-hand
side of the housing and, conversely, a speed increase takes place
with actuation of the pushbutton on the right-hand side of the
housing, with simultaneous actuation of the pushbutton 60. Since in
the case of a screwdriver or drill, two-handed actuation is not
required for safety reasons, three pushbuttons or assigned
switching elements are therefore sufficient for this, in order to
make starting-up of the tool and speed adjustment possible. Here,
too, the controller 48 is preferably designed in such a way that a
speed adjustment only takes place if the speed sensor receives a
speed signal, and consequently the motor or the drive shaft is
rotating.
In addition or as an alternative to the speed adjusting
possibility, this power tool 50 may then have an electronic
change-over possibility for right-hand/left-hand rotation. For this
purpose, once again two pushbuttons by means of which the assigned
switching elements can be actuated are provided on the left-hand
and right-hand sides of the housing. Of course, in FIG. 3 only the
pushbutton 66 on the left-hand side of the housing can be seen,
while the opposite pushbutton on the right-hand side of the housing
is hidden. These pushbuttons are significantly offset forward from
the other pushbuttons 62, in order to avoid inadvertent actuation
and to provide logical separation between the pushbuttons 62 for
speed adjustment and 66 for setting right-hand/left-hand
rotation.
The arrangement can then be set up in such a way that, with
simultaneous actuation of the pushbutton 60 and the pushbutton 66
on the left-hand side of the housing and with the motor stationary,
switching over to left-hand rotation takes place if left-hand
rotation is not already set. If, on the other hand, the pushbutton
60 and the pushbutton opposite from the pushbutton 66 on the
right-hand side of the housing are actuated simultaneously, the
changeover to right-hand rotation takes place if right-hand
rotation is not already set.
If, with the motor running, one of the pushbuttons 66 on the
left-hand side of the housing or on the opposite side of the
housing is actuated, the motor is firstly run down by the
controller and then the switching-over to the other direction of
rotation is performed. Alternatively, the arrangement could also be
set up in such a way that switching-over between right-hand and
left-hand rotation is only made possible when the motor is
stationary, i.e. the speed sensor does not receive a signal
(n=0).
* * * * *